The main work of electric power department is lightning protection of electric power transmission line, and lightning disturbance is still one of the important factors that influence the safety of electric power grid. The impulse flashover, caused by electric power transmission line be struck by lightning, causes flashover of circuit insulator string, then produces great power frequency freewheeling and damages the insulator string and fitting, results in line accidents. Because of its limitation, the ‘blocked’ lightning protection which is used conventionally cannot absolutely solve the accidents caused by lightning. So in order to protect the electric power transmission line, the electric power department generally sets parallel protection gap or line-arrester on the line. However, in practice, the parallel protection gap and line-arrester have some obvious defects as following:
At first, when the electric power transmission line is struck by lightning, the parallel protection gap will be punctured preferentially by overvoltage caused by the lightning, and conduct the lightning current to earth, so as to protect the line and electrical appliance. However, because of the parallel protection gap lacks the capability of arc extinguishing, it cannot extinguish the power frequency freewheeling caused after the flashover of insulator string, arc burns in the protection gap for a long time, this will damage the insulator string, and even cause the electric power transmission line to disconnection, and the arc will erode electrode and weaken its protection performance at the same time. In the end, depending on circuit breaker to extinguish arc for the protection of electric power transmission line and appliance, this is a way that sacrifices trip-out rate and reliability of power support for low accident rate.
Then, line-arrester is expensive, and it has high costs of use and maintenance, large leakage current, short service life, frequent replacing, and the zinc oxide module used in line-arrester exists obvious skin effect when struck by lightning, the large electric current makes it explodes easily, consequently breakdown of line for a long time, this goes against the economical, safe and stable operation of electric network.
So people begin to study the above problems, for example, the inventor's patent applied before (Chinese patent number: 2011201046273), disclosed a 10-35 kV overhead transmission line constrained space gas injection arc extinguish lightning protection gap device which is suitable for 10-35 kV overhead transmission line, the device is parallel connection stalled at the two ends of circuit insulator string, the flashover voltage between protection gaps is lower than that of insulator string protected, so as to be preferentially punctured before the insulator string protected when the electric power transmission line is struck by lightning, when the electro-discharge occurs, which caused by puncture, thunder and lightning pulse acquisition device auto-induces lightning current signal and triggers high-speed spray gas generating device, the high-speed spray gas generating device instantly generates high-speed spray gas flow to intensively concuss the freewheeling arc in constrained space in the longitudinal direction, and make the freewheeling arc cooling and extinct. Another example (Chinese patent number: 2011200053246) disclosed a transmission line constrained space gas flow injection arc extinguish lightning protection gap device which is suitable for any voltage level. The device is parallel installed at the two ends of circuit insulator string, the flashover voltage between protection gaps is lower than that of insulator string protected, so as to be preferentially punctured before the insulator string protected when the electric power transmission line is struck by lightning, when the electro-discharge occurs, which caused by puncture, gas generating material which is in the constrained space is heated sharply by arc with high temperature, at the same time thunder and lightning pulse acquisition device acquire signal automatically and start spray gas generating device, the spray gas generating device instantly generates high-speed gas flow which strongly impacts on the flaming arc length-ways, cools it down and finally extinguishes it. The patents mentioned have achieved good effect in solving the above problems, however as to higher voltage level or larger short-circuit current arc, especially for the phenomenon that the direct current arc does not exist arc zero and the wire will be burned by arc, and protection gap electrode is easily burned by arc in a case where there is no arc extinguish gas capsule, in order to solve the problems, besides increase the power of arc extinguish gas capsule, we must give a method and principle that can weaken current arc, prevent wire from burning and prevent gap electrode from being burned by arc, so that it can achieve better effect on arc extinguishing, and improve the stability of power system. Therefore, a lightning protection gap protecting device with more reliable performance and wider range of application is in badly need on the market, the device can prevent the wire from being burned by arc even in a case where there is a phenomenon that the direct current arc does not exist arc zero.